The invention is related to an ethylene oxichlorination process in the presence of a catalyst the efficiency of which is remarkably improved by the use of an especially designed reactor which maintains a fluid catalytic bed in the reactor tubes by the use of a cap ferrule and a fixed bed of granulated nickel.
Most of the known processes for halogenation of aliphatic hydrocarbons and in particular to obtain 1,2 dichloro ethane are generally carried out through direct chlorination of ethylene or through oxichlorination of ethylene.
The direct chlorination of ethylene to produce 1,2-dichloro ethane is conducted in a liquid phase reactor by mixing intimately ethylene and chlorine in liquid dichloro ethane. In general, these reactions are conducted in the presence of catalysts such as ferric chloride.
Oxichlorination of ethylene to produce 1,2 dichloro ethane is also carried out in reactors, in the presence of fluid or fixed catalytic beds, under moderate temperatures and pressures. The catalysts used in this type of reaction are in most cases copper based, such as copper chlorides and sodium or potassium chloride, deposited on an adequate support. Other types of catalysts are also known which are constituted by rare earths metallic chlorides, sulphate salts and ferric chloride.
As for the operating conditions, it happens that at temperatures above 300.degree. C. secondary reactions usually take place, deactivating the catalyst used when same undergoes a higher coking; the sublimation of copper is also undesirably increased. The by-products formed by secondary reactions during oxichlorination of ethylene are in general vinyl chloride, ethyl chloride, 1,1 dichloro ethane, trichloroethylene, methylene chloride, etc. These by-products are formed depending on the selected process and all of them cause problems in the obtainment of 1,2 dichloro ethane.
According to the prior art, there exist at the present time several processes to obtain chlorinated hydrocarbons, such as the processes of B. F. Goodrich, PPG Industries, Inc., Rhone-Poulenc, S.A., Monsanto Co., etc.
The Goodrich process produces dichloro ethane from ethylene, chlorine and air, through the stoichiometric reaction: EQU CI.sub.2 +C.sub.2 H.sub.4 .fwdarw.C.sub.2 H.sub.4 CI.sub.2
or by means of oxichlorination of: EQU C.sub.2 H.sub.4 +2HCI+1/2O.sub.2 .fwdarw.C.sub.2 H.sub.4 CI.sub.2 +H.sub.2 O
The latter reaction is conducted in a fluid bed of a copper chloride catalyst. The reaction is carried out in a specially designed reactor made of carbon steel.
The PPG Industries, Inc. process is conducted in a direct chlorination unit, combining chlorine and ethylene in a liquid phase in accordance with the reaction: EQU C.sub.2 H.sub.4 +CI.sub.2 .fwdarw.C.sub.2 H.sub.4 CI.sub.2
or in an ethylene oxichlorination unit in which oxygen and HCI are reacted in a vapor phase in the presence of a catalyst developed by PPG, in accordance with the reaction: ##STR2##
The raw dichloro ethane of both processes is combined with the recycled dichloro ethane in the pyrolysis unit and is purified by distillation.
The Rhone-Poulenc, S.A. process produces dichloro ethane either by direct chlorination where chlorine is reacted with ethylene in liquid dichloro ethane in accordance with the reaction: EQU C.sub.2 H.sub.4 +CI.sub.2 .fwdarw.C.sub.2 H.sub.4 CI.sub.2
or through oxichlorination of ethylene in accordance with the reaction: EQU C.sub.2 H.sub.4 2HCI+1/2O.sub.2 .fwdarw.C.sub.2 H.sub.4 CI.sub.2 +H.sub.2 O
The oxichlorination process is a vapor phase reaction which is conducted in a carbon steel reactor that operates under moderate pressures.
In the direct chlorination process, the ethylene and chlorine gases are loaded into the reactor which contains liquid dichloro ethane as a reaction medium and cooling system, and the dichloro ethane which is produced is treated thereafter to withdraw the chlorine and HCI content. The raw dichloro ethane is purified by distillation.
Other known techniques such as the Stauffer process produce dichloro ethane either by direct chlorination of ethylene where ethylene and chlorine are reacted in a liquid phase and under controlled reaction conditions, the obtained product is combined with the oxichlorination product, and then it is washed and distilled, or the dichloro ethane is obtained by the combination of the oxi reaction with the HCI recycle, fresh ethylene and air in a fixed catalytic tubular reactor, or else by the modified process of oxichlorination of ethylene based on oxygen, where the condensed dichloro ethane is compressed and recirculated to the first oxi reactor, using an excess of ethylene to increase the HCI conversion and to decrease the formation of by-products.
Among other technologies which are known for the obtainment of dichloro ethane, there are the MTC Chemical Technology process, and the Toyo Soda Technology.
The MTC technology uses a boiling liquid process for the direct chlorination reaction where the reaction heat is dissipated with an outgoing stream of gaseous dichloro ethane which is externally condensed and sent to purification.
The MTC technology also uses the oxichlorination process, and it is characterized by the use of oxygen batches and a fluidized bed reactor, the effluent gases from the reactor being cooled rapidly with circulating dichloro ethane followed by a caustic neutralization.
The Toyo Soda process is similar to the one developed by the Stauffer technology, its main differences being the use of an absorber-separator on the gas effluent of vent oxi and the dehydration of the raw dichloro ethane before the purification.
Monsanto Technology--This process is similar to the Stauffer technology, and it is based on recirculating the HCI produced in the vinyl chloride plant to an oxichlorination reactor. The process may be carried out in the same manner as those mentioned before, that is by direct chlorination or by oxichlorination.
The Monsanto oxichlorination process is a vapor phase reaction and it is carried out in a carbon steel reactor which operates at moderate pressures, in the presence of a fluid bed catalyst.
The efficiency of processes that are carried out in reactors varies depending on the design of the chosen reactor. Reactors may be fixed bed catalytic reactors or fluidized bed catalytic reactors; in general, it has been observed that the fluidized bed reactors provide a better ethylene conversion (94-97%), of HCI (95-97%), and a better selectivity of 1,2 dichloro ethane (94-96%), than the fixed bed reactors. These efficiency results are also subject to the type of reactor design used and to the quality of the raw materials employed.
The fluidized bed oxichlorination reactors generally comprise diffusing elements for the reaction gases made of porous plates which perform an adequate distribution of the gases, such porous plates being commonly known as ferrules and constituted by a porous plate with a filtering element.
The known reactors that operate with this type of ferrules present some disadvantages in their use due to the fact that the porous plate is only useful for clean feed gases, from the known experiences in plants of chlorinated derivatives it is observed that the stream of anhydrous HCI which results from the pyrolysis of 1,2 dichloro ethane is not completely clean in spite of its filtration before its use; this causes in a period of 3 to 4 months of use of the porous plate ferrule a plugging of the filter as well as of the porous plate.
The plugging of the porous plate and the temperature difference between the operating temperature of approximately 180.degree. C. and the subsequent cooling of the reactors are factors that cause the premature breakage of the porous plate.
The plugging of the porous plate also causes a decrease of the fluidification speed which results in the compression of the catalyst in the reactor tubes; this phenomenon causes the increase in the formation of secondary reactions which affect the efficiency of the process.
The applicant has developed a process to obtain 1,2 dichloro ethane which is more efficient, by the oxichlorination of ethylene in a tubular reactor which comprises a gas diffusor that is especially designed with a cap ferrule which is improved by the incorporation of a nickel granule bed that constantly maintans a fluid catalyst during the reaction. Under these conditions, it is not necessary to make a previous purification of the raw materials, particularly of the HCI stream.
There being no plugging of the ferrule, the formation of secondary reactions created by the compression of the catalyst is avoided, and consequently the efficiency of the process is considerably increased.